2 EMPTY COMEDIES FROM FOX

Clifford Terry, TV/radio criticCHICAGO TRIBUNE

Two new Fox Broadcasting Co. comedy series make their debuts Saturday, but it is doubtful that years from now patrons of the Museum of Broadcasting will be lining up to demand vintage tapes of ''Karen`s Song'' or ''The New Adventures of Beans Baxter.''

In the former, which airs at 8:30 p.m. on WFLD-Ch. 32, Patty Duke stars as Karen Matthews, a divorced 40-year-old who has a new condo in Los Angeles, a new job as an editor at a publishing house and the same old daughter (played by Terri Hatcher), now a UCLA freshman. Karen also has a new beau, and that`s the flimsy premise upon which this dreary series hangs its hat. The light of her life, Steven Foreman (Lewis Smith of ''North and South Book II'' and

''Buckaroo Bonzai''), sells sandwiches in her office building to promote his catering company, archly named A Tasteful Affair. More to the point, he is 28 years old, setting up an age-differential affair that, while not May-December, is certainly Arbor Day-Labor Day.

In the opener and subsequent episodes, we learn that Karen tries to hide her age--and her daughter`s--from Steven, whom she has fondly dubbed ''Baby Face Nelson.'' Explaining to friends why she didn`t invite him to her 40th birthday party, she says, ''I didn`t want to see his face when they brought that cake out, blazing like the torch of freedom.'' (Her best friend and colleague, not so incidentally, is played by the overbearing, insufferable Lainie Kazan.)

We also learn that Karen finally spills the truth to Steven and that he is an absolute brick about it--which is not surprising because we also learn that not only does he create perfect eggs Benedict, read Japanese, play a hard-nosed game of tennis and unhesitatingly work the crossword in the New York Times Magazine, but he is sensitive, caring and unflappable. It`s as if the `60s had bumped into the `80s and concocted an upwardly mobile flower child.

Meanwhile, when the mother-career woman is not busy demonstrating her, yes, vulnerability, she seems to be making a career of avoiding work. In the three episodes previewed, she settles down to her editing chores for about 10 seconds.

Someone certainly should have put a pencil to the scripts for this series, created by Linda Marsh and Margie Peters (''The Facts of Life,''

''Valerie'') although, admittedly, the writing is consistent; there isn`t a single genuine laugh all the way through. On the other hand, Duke fails to draw upon the tenacity and spunkiness that has gotten her through roles from Helen Keller to Patty/Cathy Lane to Martha Washington, perhaps recognizing early on that this particular vehicle is no ''Mary Tyler Moore Show,'' ''Molly Dodd'' nor even ''Rhoda.''

Surely, to dismiss ''Karen`s Song'' as a clinker--a kind of ''Jeannie One-Note''--is extremely facile, but there it is.

Fox Broadcasting, though, seems to have the touch when it comes to programming for adolescents. Junior-high-school types have gone batty for ''21 Jump Street'' since its debut in the spring, and last week they were agog over ''Werewolf,'' despite the presence of Chuck Connors, his eye patch and middle-European accent.

Now comes ''The New Adventures of Beans Baxter'' (7 p.m. on Channel 32), which concerns a Ricky Nelson/squeaky-clean-type 16-year-old high school student who not only experiences culture shock when his family picks up and moves from Witches Creek, Kan., to Washington, D.C., but becomes entangled in international espionage.

Seems that Benjamin ''Beans'' Baxter (Jonathan Ward) has a father who passed himself off as a postal worker while working as one of the top undercover operatives in the nation for the Network, a postal service for the federal government`s secret agencies. But after the move to D.C., the senior Baxter is stealthily abducted by the dastardly--and, predictably, bumbling

--terrorist members of the Underground Government Liberation Intergroup

(UGLI), who simultaneously stage an explosion in which he apparently is killed. (The event triggers a curious lack of emotion. Watching his father`s postal truck being blown to bits, Beans feebly mutters, ''I`m sorry, Dad.''

Later, he views the rerun on the late news with his mother--played by Elinor Donahue, known years ago as ''Princess'' on ''Father Knows Best''--and they both shrug it off as if it were just another mishap.)

Beans seems more concerned with putting the moves on an exotic, Keane-eyed classmate at his upper-crust suburban school, one Cake Lase (Karen Mistral). However, after an ''incredible bureaucratic screw-up,'' he takes over as courier for his father and is entrusted with a 12-megaton plutonium firing cap that UGLI is trying to swipe. Segueing into a double life as spy and student, he promptly makes use of his pet guinea pig, which he hooks up to a video camera--''the world`s first guinea-cam.''

Created by someone actually named Savage Steve Holland, ''Beans Baxter,'' like ''Werewolf,'' is, in effect, a Saturday evening cartoon. The one worthy bit comes late in the hour, when the terrorists are torturing another abductee by showing continuous slides of baby pictures. It`s a nice moment but not as nice as the one in ''Top Secret,'' in which another prisoner is being interrogated. The instruments of torture: the paintings of Leroy Neiman.